Fracture behaviour of compact tension specimens of nickel-based single crystal under tension creep and cyclic loading

The fracture behaviour of compact tension (CT) specimens of nickel-based single crystal superalloys DD3 was studied at 950, 850, 760°C. The creep and fatigue property was investigated at 950°C. Three crystallographic orientations [001], [011] and [111] of the specimens were considered. The macro crack growth and micro characterization of the fracture surfaces were examined by the optical microscope (OM) and scan electron microscope (SEM). The tension experimental results show that the macro crack growth path takes place in specific vectors and appears to be in a zigzag manner. The temperature has much influence on fracture behaviour. At low temperature (760°C), the fracture mode is pure shear fracture and belongs to brittle mode. But at high temperature (950°C), fracture mode turns to be microvoid coalescence fracture and belongs to ductile mode. The creep and fatigue properties of CT specimens are-obviously anisotropic. Creep life decreases in the order of [011], [111], [001] and fatigue life decreases in the order of [111], [011], [001] under same test conditions. The creep and fatigue crack growth path is perpendicular to the loading axis. It is found by SEM that there are much cup-cone dimple on the creep fracture and typical fatigue striations on the fatigue fracture surface. The fracture damage can results in crack growth more easily than creep damage.